374 Report of the Mycologist of the 



will at once apply the remedy as recommended and thereby make 

 cucumber growing as profitable as it was before the disease ap- 

 peared; but, judging from the history of the treatment of plant 

 diseases in this country, it seems probable that it will be several 

 years before the spraying of cucumbers will become anything 

 like a general practice. In the meantime those who do spray 

 will reap a harvest, for, in all probabilit}^, the disease will con- 

 tinue to spread and become s'o destructive as to drive many 

 growers out of the business, and thus keep up prices. While, in 

 any given locality, the disease may fluctuate in virulence from 

 year to year with the weather conditions, it is • undoubtedly in 

 America to stay and may be expected to cause heavy losses in 



every year. 



EXPLANATION OF PLATE XI. 



Fig. 1. Cross-section of a cucumber leaf. 

 a. Epidermis of the upper surface. 

 a/. Epidermis of the under surface. 

 &.&. Palisade cells, 

 c. A chlorophj'll grain, 

 w. Oross-section of a stoma. 

 i. Intercellular passage. 

 Fig. 2. Surface section from the under surface of a cucumber 

 leaf. 



s. A stoma. 



r. The rift or opening between the two crescelit-shapcd 

 guard-cells of the stoma. 

 Fig. 3. A plant hair (trichome) from the under surface of a 

 cucumber leaf. 



Note. — All the figures on this plate were drawn with the aid 

 of an Abbe camera lucida under a magnification of 700 diameters 

 and afterwards reduced by the engraver to the present magnifi- 

 cation, viz.: 465 diameters. 



EXPLANATION OF PLATE XII. 



The cucumber downy mildew {Plasmopara cuhensis). 

 Fig. 1. A vigorous sporophore grown on a cucumber leaf whicli 

 had been kept twenty-four hours in a moist chamber. (Original.) 



